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Analysis

Summary

FNB should have been reported as potential traffic to the crew of FNA since its track was planned to be within 15 NM laterally of FNA's route and because it was climbing through FNA's level.

The flight service officer reported that he would have normally passed traffic information to the pilots when FNB taxied at Carnarvon. However, on this occasion, he did not recognise that the two aircraft were potentially conflicting traffic. Having calculated a release time of 0225 when he expected FNB to be above FL200, in controlled airspace and therefore clear of FNA, he may have assumed that the traffic had no potential for conflict. An indication of his assumption was that he filed the flight strip for FNB soon after the release time; therefore, the potential for conflict of these two aircraft was never recognised by the flight service officer.

The flight service officer did not have a history of inadequately passing appropriate traffic information although he had, on occasion, used inappropriate air traffic control procedures.

The incident probably occurred as a result of a combination of factors. Firstly, the flight service officer reported that he was pre-occupied with his personal situation and was tired. As a result, he probably did not adequately monitor the progress of his routine actions. Secondly, he reported that he might have used a presumed rate of climb for the Fokker 50 as a basis for determining whether the traffic was potentially conflicting. Such a calculation was erroneous and irrelevant because the traffic assessment criteria in the Manual of Air Traffic Services required the traffic information to be passed. The use of this calculation may have been a manifestation of the flight service officer's occasional use of inappropriate procedures. His pre-occupation, tiredness and deviation from standard operating procedures may have contributed to the flight service officer losing situational awareness and as a result, he did not recognise that the flight paths of FNB and FNA were potentially conflicting.

Once the flight service officer had committed to not advising the crews of FNB and FNA of each other's presence, there were no organisational defences available, such as active supervision, to preclude the mistake going unnoticed. As a result, once the flight service officer had made the error, there was no backup.

Because the pilot in command of FNB did not need to take any avoiding action, it is unlikely that the provision of TCAS stopped an accident from occurring. However, the fact that TCAS had alerted the crew of FNB to the close proximity of traffic unknown to them indicated that it would have been the only defence available had the two aircraft been on a collision course. The effectiveness of TCAS in alerting and directing the crew of FNB to proximal traffic also illustrated the weakness of the principle of see-and-avoid.

CONCLUSION

The flight service officer was fatigued and distracted, probably as a result of stress and inadequate rest before commencing his shift. Consequently, he did not adequately monitor the progress of his routine actions and he did not notice that the two aircraft were potentially conflicting traffic. He did not provide traffic information to the pilots of the two aircraft as required by Manual of Air Traffic Services.

 
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